From Fashionably Geek: In case you haven’t noticed, realistic Stromtrooper helmets are pretty expensive. Fortunately, you can make one on the super cheap using two gallon-sized milk jugs. The process outlined by the blog Filth Wizardry is actually pretty simple, so much so that it would make a great project for kids.
Make sure to clean those bottles out thoroughly though. A helmet full of sour milk could get real nasty, real fast. Should probably use water jugs instead.